1. Field of the Invention
This invention relates to systems and methods of preventing contamination of a contaminant-free media volume and more particularly relates to a fluid media particle isolator between a contaminant-free media volume and a contaminated particle generating media volume.
2. Background Information
There is a requirement in some industries and applications to maintain a containment-free environment. This requirement means that there must be an isolation and separation of contaminated media from containment-free media. The processing of wafers to manufacture semiconductors is a good example of this requirement. Particles that might contaminate the wafers from which semiconductors are built must be kept isolated.
The wafers from which semiconductors are built are stored in large contaminant-free enclosures known as storage and transfer systems. The wafers stored in contaminant-free containers or moved in and out of the storage area by machinery known as a transfer system. The transfer systems use linear and rotary activators to transfer the wafers to and from the storage area. These actuators necessarily generate particles that can contaminate the wafers. The contamination of the wafers from these particles is a major cause of device failure and rejection during the manufacturing process.
Accordingly there are many techniques employed to isolate the media around the wafers from the media where the particles are generated by the machinery. One technique scavenges the area around the machinery where particles are generated with a vacuum.
This technique does somewhat reduce the migration of particles from the area of contaminated media to the containment-free media area. However a disadvantage and limitation of this vacuum technique is that a flexible mechanical separation is needed between the containment-free (clean zone) media area containing the wafers and the contaminated area of mechanical equipment which generates particles. The flexible mechanical separation is usually a sealing band made of flexible plastic or metal. The sealing band must be flexible to allow a mechanical actuator to transmit work such as moving wafers to and from storage. An identified problem of using the flexible mechanical band to create a differential pressure for the vacuum to be effective and help mechanically isolate contaminating particles from the wafers is the mechanical band produces contaminating particles when the mechanical actuator passes through the band.
The current state of the art for media isolation to prevent contamination includes the use of a physical barrier between the contaminant-free media volume and an adjacent media volume that may contain contaminates. These barriers either involve movable mechanical parts or encounter movable mechanical parts. When moving mechanical parts make contact or rub against one another they invariably produce particles that can contaminate a contaminant-free media volume. One example of such a system is disclosed and described in U.S. Pat. No. 5,615,988 of Weisler et al issued Apr. 1, 1977. This patent discloses a wafer transfer system having moving transfer system to transfer wafers from carriers in a storage area. A door in a wall separates the storage area from the transfer area. The door is opened to provide access to wafers in a storage carrier. The transfer system moves through the door to retrieve wafers. All these moving parts are going to cause a release of particles, known generally as xe2x80x9cwearxe2x80x9d, that can contaminate the wafers.
In the case of the mechanical seals described above, they are flexible to allow a transfer mechanism to move from one media volume to another to retrieve wafers. These parts rub together and produce contamination. Attempts to prevent the contamination involve creating a differential pressure by increasing pressure or applying a vacuum to one media volume. The combination of the mechanical seal with the differential pressure in most common applications creates a bias and establishes an unidirectional flow from one media volume to an adjacent media volume. Generally this is away from the contaminant-free media volume and toward the contaminated particle generating media volume. While these methods help they are not entirely effective to prevent a back flow of contaminating particles from entering the contaminant-free media volume particularly when the mechanical seal makes contact with the transfer mechanism.
It is thus one object of the invention to produce a fluid media isolator that differs from current state of the art devices by having no contacting, sliding, or rubbing parts when a transfer system actuator arm moves.
Another object of the present invention is to have a fluid media isolator that transfers clean media from the particle free (clean zone) wafer process area toward the particle generating contaminated (dirty zone).
Yet another object of the present invention is to provide a fluid media isolator that mechanically isolates a contaminant-free zone and a contaminate generating zone with a barrier comprises of tortuous media zone.
Still another object of the present invention is to provide a fluid media isolator on both sides of a transfer system actuator arm for forward or reverse travel with a linear actuator.
In yet another object of the present invention the fluid media isolator is mounted on both sides of an actuator arm for clockwise and counter-clockwise movement for a radial actuator.
Yet another object of the invention is to provide a device for isolating one volume of media from an adjacent volume of media that have a common connection between them.
Another object of the invention is to provide a device that can transfer media from one volume to another volume in a unidirectional manner while biasing back flow from one volume to another.
Still another object of the invention is to provide a fluid media isolator that can transfer and mix one media volume with another and pump in one direction.
Still another object of the invention is to provide a fluid media isolator comprised of a tortuous path separating a contaminant-free media volume from a contaminant generating volume and a fluid transfer device intersecting the tortuous path mounted for movement with the transfer system.
Another object of the present invention is to provide a fluid transfer device comprised of a plurality of vessels or cells that transfer fluid media from one vessel to another that is mounted in a tortuous path for movement with the transfer system actuator. The fluid transfer device pumps unidirectionally with each movement of the transfer device to establish unidirectional flow with substantially no backstream preventing any particles generated by a drive system for contaminating the containment-free media volume.
The purpose of the present invention is to provide a system and method of isolating contaminant-free media volume from a particle generating and contaminated media volume.
The system and method of the invention separates and transfers volumes of media of one mechanically separated zone to another media volume. The media volumes are separated by a pair of adjacent walls having a tortuous or serpentine path formed between them. The tortuous path is formed by alternating interleaving partitions or fins on the inside surfaces of the walls. The alternating partitions extend the full length of the wall forming a media volume in the tortuous path between the walls. The walls separate the contaminant-free media volume or zone from the contaminated volume and has an entrance at one end communicating with the contaminant-free media volume and an exit to the contaminated media volume at the opposite end. Thus the space in the wall forms a continuous tortuous path between the two media zones.
A pump is formed by a series of vessels or cells coaxially integrated in the tortuous path between the walls. The series of vessels or cells are mounted on the wafer transfer actuator arm for reciprocating linear travel within the tortuous or serpentine path between the walls. The series of vessels form an impeller that propels media from the contaminant-free zone toward the contaminated zone as it moves up and down between the walls with movement of the transfer system actuator arm.
The series of vessels or cells of predetermined length offset vertically or axially from each adjacent cell and horizontally from the entrance of the tortuous path toward the exit. Each cell has an entrance and an exit with the outer wall in close proximity but spaced from the walls and partitions the tortuous path. There are no part that can make contact or web together. The cells are arranged so an exit from one cell dumps fluid media into the adjacent cell. Each cell entrance is open at the top with a slightly larger exit transitioning to and directing or dumping media into the adjacent cell. A contoured surface of baffle in each cell provides a transition to enhance the flow of media from the entrance to the exit to dump its volume of media into the adjacent cell. The construction of the series of vessels or cells each being open to the media in the tortuous path, and offset axially and having a contoured transition surface in each cell biases and promotes flow only in the direction from the entrance to the exit with substantially no backstream or migration of contaminating particles into the contaminant-free media volume.
The system when tested showed zero migration of contaminants from the contaminated media volume to the contaminant-free media volume. This indicates that there were either no contaminating particles flowing to the contaminant-free media volume or there were so few particles that they could not be accurately detected. Thus a system with substantially no moving parts itself and moved only by its connection to the mechanics of the wafer transfer system has proved to be an effective and outstanding media isolating barrier.
In a second embodiment the fluid media transfer system is formed of a pair of intersecting cylinders having alternating circular interleaving partitions forming a circular tortuous path. The outer cylinder has a skirt fitting over the inner cylinder forming an entrance into the tortuous path formed by the series of attenuating circular partitions. A drive system is mounted at the center of the cylindrical tortuous path surrounded by a plurality of vent holes providing an exit for media drawn through the tortuous path.
Interestingly it was found that the cylindrical system works by rotation of one of the cylinders relative to the other to draw media from preferably a contaminant-free media volume for discharge through the vent holes to a non-contaminant-free volume. The partitions themselves that form the tortuous path act as impellers to propel the media from the entrance toward the exit or vent holes.
In an alternative embodiment of the cylindrical isolator, an impeller constructed of arcuate vessels of cells circumferentially offset could be integrated into the tortuous path. Each vessel or cell would have an entrance and an exit dumping into an adjacent cell except for the first and last cells. The series of cells would fit the contour of the tortuous path but be spaced sufficiently away from the walls of the tortuous path to prevent any contact that might generate contaminating particles.
In the latter embodiment the series of vessels or cells forming the impeller would be rotated or reciprocated within the tortuous path of the cylindrical isolator generating substantial flow from the entrance through to the exit or next holes.
The above and other objects, advantages, and novel features of the invention will be more fully understood from the following detailed description and the accompanying drawings, in which: